Preheat the oven to 375°F and place the racks in the bottom third and top third positions. Prepare a 13x9 inch baking dish by spraying the bottom and sides with nonstick cooking spray.
For the shrimp, add butter to a large, nonstick pan and melt over medium heat. Add the shallots and ¼ teaspoon salt and cook until translucent, for 3-4 minutes. Add the garlic and cook for an additional 1 minute until fragrant. Add in the pieces of shrimp, Old Bay, and ½ teaspoon salt and cook for 1 minute, stirring. (You do not want to cook completely at this step, as they will continue to cook in the oven.)
Remove the shrimp from the heat and add to a medium bowl and stir in the crab.
For the ricotta filling, stir together the ricotta, drained spinach, lemon juice, zest, parsley, and ½ teaspoon salt.
For the bechamel, in the same pan used for the shrimp, set over medium heat and melt the butter. Once melted, sprinkle the flour over the butter and whisk until a paste forms and cook for about 2 minutes to cook out the raw flour taste. Slowly stir in the white wine, whisking vigorously, followed by the half and half. Stir in the clam juice, nutmeg, hot sauce, and 1 ½ teaspoons salt and let it come to a simmer, stirring occasionally. Do not boil. The sauce is ready when it has thickened and can coat the back of the spoon without being too runny. Remove from the heat and taste for seasoning and adjust to your taste.
For the shredded cheese mixture, combine all cheeses into a medium bowl and toss together.
To assemble, spoon ½ cup of the bechamel sauce into the prepared baking dish. Stir the shrimp mixture and the herbs into the remaining bechamel sauce. In the dish, top the bechamel sauce with sheets of lasagna. Next, spread on one-third of the ricotta mixture, followed by one-third of the bechamel, then top with a third of the shredded cheese. Again, top with lasagna noodles, ricotta, bechamel, then cheese. For the last layer, add noodles, ricotta, then sprinkle the final third of shredded cheese covering the top.
Cover with foil, place on a baking sheet, then place on the bottom third rack and bake for 40-45 minutes. Remove the foil, then move the pan to the top third rack and continue baking for an additional 10-15 minutes, until the top is bubbly and brown.
Remove from the oven, sprinkle with the remaining parsley, and let sit for 15 minutes. Then serve and enjoy immediately.